1. Field of the Invention
The present invention relates to soft magnetic films which contain a CoFeα alloy (the element α is Ni or the like) used as, for example, core materials of thin-film magnetic heads and which have superior corrosion resistance and a higher saturated magnetic flux density Bs than an NiFe alloy. In addition, the present invention relates to thin-film magnetic heads using the soft magnetic films described above, to methods for manufacturing the soft magnetic films, and to methods for manufacturing the thin-film magnetic heads.
2. Description of the Related Art
In particular, concomitant with the recent trend toward higher recording densities, it has become necessary that, in order to improve a recording density, a magnetic material having a higher saturated magnetic flux density Bs be used for forming a core layer of a thin-film magnetic head so that a magnetic flux is concentrated in the vicinity of the gap of the core layer.
An NiFe alloy has been frequently used for the magnetic material described above. The NiFe alloy described above is formed by an electroplating method using a DC current and is able to have a saturated magnetic flux density Bs of approximately 1.8 T.
In order to further increase the saturated magnetic flux density Bs of the NiFe alloy, for example, an electroplating method using a pulse current is used in place of an electroplating method using a DC current.
According to the method described above, the Bs of the NiFe alloy can be increased; however, the saturated magnetic flux density Bs cannot be increased to 2.0 T or more. In addition, the surface roughness of the film is increased, and hence, there has been a problem in that the NiFe alloy is corroded by various solvents used in a process for forming a thin-film magnetic head.
From the NiFe alloy described above, a soft magnetic film having a high saturated magnetic flux density Bs together with superior corrosion resistance has not been formed.
In addition to the NiFe alloy, as a soft magnetic material which is frequently used, a CoFe alloy film may be mentioned. When the component ratio of Fe is appropriately controlled, the CoFe alloy film may have a higher saturated magnetic flux density Bs than that of an NiFe alloy film; however, it has the following problem.
Depending on the structure of a thin-film magnetic head or another magnetic element, an NiFe alloy may be overlaid on the CoFe alloy in some cases. In the case described above, when the NiFe alloy film is formed on the CoFe alloy film by an electroplating method, the CoFe alloy film may be ionized and dissolved out, and as a result, corrosion occurs.
The reason for this is that a significant potential difference (difference in standard electrode potential) is generated between the CoFe alloy film and the NiFe alloy film, and it is believed that a so-called battery effect is obtained by this potential difference and that the CoFe alloy film is dissolved out.
In addition to the NiFe alloy film and the CoFe alloy film described above, a CoFeNi film is also one of the soft magnetic films which are frequently used. For example, in Table 2 shown in U.S. Pat. No. 6,063,512, four CoFeNi alloy films having different compositions and soft magnetic properties thereof are listed.
However, according to the compositions of the CoFeNi alloy films described in this publication, the saturated magnetic flux densities Bs thereof are all less than 2.0 T, and compared to a NiFe alloy film, a large saturated magnetic flux density Bs cannot be effectively obtained.